Heavy element loaded polymer composites have long been proposed to detect high energy X- and -rays upon scintillation. The previously reported bulk composite scintillators have achieved limited success because of the diminished light output resulting from fluorescence quenching and opacity. We demonstrate the synthesis of a transparent nanocomposite comprising gadolinium oxide nanocrystals uniformly dispersed in bulk-size samples at high loading content. The strategy to avoid luminescence quenching and opacity in the nanocomposite was successfully deployed, which led to the radioluminescence light yield up to 27,000/MeV, about twice as much as standard commercial plastic scintillators. Nanocomposites with 31 wt.% loading of nanocrystals (14 mm diameter by 3 mm thickness) generated a photoelectric peak for Cs-137 gamma (662 keV) with 11.4% energy resolution.